(a) Field of the Invention
The present invention relates to a technique for fixing a permanent magnet in a rotor. More particularly, the present invention relates to a technique for fixing a permanent magnet in a rotor core of a drive motor of an electric or hybrid vehicle.
(b) Description of the Related Art
Generally, a hybrid electric vehicle (HEV) may utilize an engine and a drive motor as a power source. A HEV drive motor typically includes a stator, which is a coil wound around a stator core, and a rotor, which may contain a plurality of permanent magnets and is located within the stator core. The drive motor is powered by a high voltage battery that is separate from a 12 V battery.
A drive motor in a hybrid or electric vehicle is normally configured to output a high speed rotational torque. If the drive motor is a permanent magnet type, the permanent magnet is located in the rotor core, and the position of the permanent magnet is carefully fixed within the rotor core so as to maintain proper balance of the rotor.
Once the permanent magnet is inserted into a slot of the rotor core, it generates a stress-point within the core as a result of centrifugal force. If the permanent magnet slips out of the slot within the rotor core during operation of the drive motor as a result of this centrifugal force, the permanent magnet, the rotor core, or both, may be damaged or broken, thereby disabling the drive motor. Consequently, it is important to ensure that the position of the permanent magnet remains fixed within the rotor core.
To solve this problem, the conventional art normally uses a resin to fill in the slot around the permanent magnet, thereby fixing the permanent magnet within the slot and reducing the likelihood that the permanent magnet will slip, and damage or break the rotor core. Unfortunately, the application of the resin or the adhesive in this conventional art method has a major disadvantage because the process of filling the slot with the resin (including, for example, the filling method, the viscosity of the resin/adhesive, and/or the force of gravity) often alters the position of the permanent magnet within the slot of the rotor core. This alteration may cause an imbalance of the rotor assembly, which may decrease the electro-mechanical efficiency of the drive motor, cause abnormal wear on the drive motor, or result in abnormal noise and/or vibration.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention.